1. Field of the Invention
The present invention relates to a technology of a wavelength selective switch.
2. Description of the Related Art
For realizing a wide passband, the signal light needed to be sharply converged on deflective elements by a light converging element. Generally, for making the light sharply-converged, a beam diameter of light when the light is incident on the light converging element is to be made large. However, to make the beam diameter large means to make an apparatus large in size.
In Japanese Patent Application Laid-open Publication No. 2004-133203, a structure which reduce the size of an apparatus in a direction perpendicular to a dispersive direction by making an arrangement such that a beam diameter of light incident on a dispersive element to be large in a dispersive direction, as compared to a beam diameter of light in a direction perpendicular to the dispersive direction, has been described.
However, in the structure according to Japanese Patent Application Laid-open Publication No. 2004-133203, the beam diameter in the dispersive direction when the light is incident on the dispersive element is large as it has been, and in this structure it is not possible to reduce the size of each optical element in the dispersive direction and the overall wavelength selective switch.